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Railways Sample Paper RRB (Assistant Loco Pilot) Sample Test Paper-18

  • question_answer
    Three wheels can complete respectively 60, 36, 24 revolutions per minute. There is a red spot on each wheel that touches the ground at time zero. After how much time, all these spots will simultaneously touch the ground again?

    A)  5/2 seconds       

    B)         5/3 seconds                  

    C)  5 seconds        

    D)         \[7.5\]seconds                           

    Correct Answer: C

    Solution :

    A makes 1 rev. per sec B makes \[\frac{6}{10}\] rev per sec C makes \[\frac{4}{10}\] rev per sec In other words A, B and C take 1 , \[\frac{5}{3}\] & \[\frac{5}{2}\] seconds to complete one revolution. L.C.M of 1, \[\frac{5}{3}\] &  \[\frac{5}{2}=\frac{LC.M\,\,of\,\,1,5,5}{H.C.F.\text{ }of\text{ }1,3,2}=5\] Hence, after every 5 seconds the red spots on all the three wheels touch the ground


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